Involvement of auxin and cytokinins in initiation of growth of isolated pea buds

Axillary buds from the second primary scale excised from 21-day-old pea (Pisum sativum L. cv. Vladan) plants were used as a model system for studying the release of buds from apical dominance. The isolated buds were transferred onto basal medium with or without a supplement of growth regulators and cultivated up to 24 h in short-term and up to 4 weeks in long-term experiments. In both sets of experiments endogenous IAA, cytokinins and the uptake of labelled zeatin were analysed. The development of buds was monitored by image analysis, estimation of their weight, and by anatomical studies. Generative meristems were found in isolated axillary buds already in 21-day-old plants at the beginning of the experimental period. The onset of bud growth was recorded as soon as 2 h after the bud excision by image analysis. The bud growth was accompanied by a rapid transient increase of the endogenous IAA level within the first 2 h, followed by an increase of iPA within 24 h. The uptake of the exogenous cytokinin ([H-3]Z) reached its peak between the 6 and 8 h after the release from apical dominance. The cytokinin analyses of both short-term and long-term bud cultures revealed the increase of free cytokinins and their glucosides, indicating de novo synthesis of cytokinins in the buds themselves.